WO2020088412A1 - Time bit-phase decoding method and device for quantum key distribution, and corresponding system - Google Patents

Abstract

The present invention proposes a polarization-orthogonalized rotary reflection-based direct-current modulated time bit-phase decoding method and device for quantum key distribution, and a corresponding system. Said method comprises: splitting an input optical pulse into first and second optical pulses; and performing direct-current modulation and phase decoding on the first optical pulse and performing time bit decoding on the second optical pulse. Performing direct-current modulation and phase decoding on the first optical pulse comprises: splitting the first optical pulse into two sub-optical pulses by means of a beam splitter, and transmitting the two sub-optical pulses along two sub-optical paths respectively, and after relative delay is performed on the two sub-optical pulses, respectively reflecting, by means of two reflection devices, same back to the beam splitter for beam combining and outputting, wherein when each of the sub-optical pulses is reflected by a corresponding reflection device, two orthogonal polarization states of each sub-optical pulse are subjected to polarization-orthogonalized rotary reflection, and one of the two sub-optical pulses is subjected to direct-current phase modulation. The present invention provides a polarization induced fading-resist time bit-phase encoded quantum key distribution decoding scheme, which is easy to implement and use.

Description

Quantum key distribution time bit-phase decoding method and device and corresponding system Technical field

The invention relates to the technical field of optical transmission secure communication, and in particular to a method and device for time-bit-phase decoding of DC modulation quantum key distribution based on polarization orthogonal rotation reflection and a quantum key distribution system including the device.

Background technique

Quantum secret communication technology is a frontier hotspot field combining quantum physics and information science. Based on the quantum key distribution technology and the principle of one-time encryption, quantum secret communication can realize the secure transmission of information in an open channel. Quantum key distribution is based on the physical principles of quantum mechanics Heisenberg uncertainty relationship, quantum non-cloning theorem, etc. It can achieve the safe sharing of keys between users and can detect potential eavesdropping behaviors. It can be used in national defense, government affairs, Areas with high security information transmission requirements such as finance and electricity.

Time-bit-phase encoding quantum key distribution uses a set of time bases and a set of phase bases. The time base is encoded using two time patterns with different time positions, and the phase base is encoded using two phase differences between the front and back optical pulses. Terrestrial quantum key distribution is mainly based on fiber channel transmission, and the production of optical fibers has non-ideal situations such as non-circular cross-section, uneven distribution of core refractive index in the radial direction, and optical fibers are affected by temperature, strain, and bending in the actual environment. Will produce random birefringence effect. Affected by the random birefringence of the optical fiber, when the optical pulse reaches the receiving end after being transmitted through a long-distance optical fiber, its polarization state will change randomly. Time-based decoding in time-bit-phase coding is not affected by changes in polarization state. However, during interference decoding, the phase-based decoding has the problem of polarization-induced fading due to the influence of the birefringence of the transmission fiber and the decoding interferometer fiber. Stability leads to an increase in bit error rate, the need for additional correction equipment, increases the system complexity and cost, and it is difficult to achieve stable applications for strong interference situations such as overhead optical cables and road and bridge optical cables. For the quantum key distribution time bit-phase coding scheme, how to perform phase interference decoding stably and efficiently is a hot spot and difficult problem for quantum secret communication applications based on the existing optical cable infrastructure.

Summary of the invention

The main purpose of the present invention is to propose a method and a device for time-bit-phase decoding of DC modulation quantum key distribution based on polarization orthogonal rotation reflection, in order to solve the time-phase-coded quantum key distribution application of phase-based decoding The problem of unstable phase decoding interference caused by induced fading.

The present invention provides at least the following technical solutions:

1. A time-bit-phase decoding method for DC modulation quantum key distribution based on polarization orthogonal rotation reflection, characterized in that the method includes:

Split an incident input optical pulse of any polarization state into a first optical pulse and a second optical pulse; and

According to the quantum key distribution protocol, performing DC modulation phase decoding on the first optical pulse and time-bit decoding the second optical pulse,

Wherein, the DC modulation phase decoding of the first optical pulse includes:

Splitting the first optical pulse into two sub-optical pulses by a beam splitter; and

Transmitting the two sub-optical pulses along the two sub-optical paths respectively, and delaying the two sub-optical pulses relative to each other, then reflecting them back to the beam splitter through two reflecting devices to combine and output the beam splitter, Wherein for each of the two sub-optical pulses:

When the sub-light pulse of this path is reflected by the corresponding reflection device of the two reflection devices, the two orthogonal polarization states of the sub-light pulse of the path are reflected by the polarization orthogonal rotation, so that after reflection by the corresponding reflection device, the sub-light pulse of the path Each orthogonal polarization state of the pulse is transformed into its orthogonal polarization state,

And wherein, during the splitting of the beam splitter to the beam splitter, at least one of the two sub-optical pulses transmitted on the two sub-optical paths is subjected to a DC phase according to a quantum key distribution protocol modulation.

2. The time-bit-phase decoding method for DC modulation quantum key distribution based on polarization orthogonal rotation reflection according to scheme 1, wherein the two reflection devices are circular polarization orthogonal rotation reflection devices, and the two Each reflecting device includes a reflecting mirror.

3. The time-bit-phase decoding method for DC modulation quantum key distribution based on polarization orthogonal rotation reflection according to scheme 2, wherein the beam splitter is a circular polarization maintaining beam splitter.

4. The time-bit-phase decoding method for DC modulation quantum key distribution based on polarization orthogonal rotation reflection according to scheme 1, wherein the two reflection devices are linear polarization orthogonal rotation reflection devices.

5. The time-bit-phase decoding method for DC modulation quantum key distribution based on polarization orthogonal rotation reflection according to scheme 4, wherein the two reflection devices each include a mirror and a quarter wave plate, The mirror is integrally formed with the quarter-wave plate at the rear end of the quarter-wave plate, wherein the polarization direction of one of the two orthogonal polarization states of the two sub-light pulses is The angle of the slow axis of the quarter wave plate is 45 degrees.

6. The time-bit-phase decoding method of DC modulation quantum key distribution based on polarization orthogonal rotation reflection according to scheme 4, wherein the beam splitter is a line polarization maintaining beam splitter.

7. The time-bit-phase decoding method for DC modulation quantum key distribution based on polarization orthogonal rotation reflection according to scheme 1, wherein the two reflection devices are elliptical polarization orthogonal rotation reflection devices, and the points The beam splitter is an elliptical polarization maintaining beam splitter.

8. The time-bit-phase decoding method of DC modulation quantum key distribution based on polarization orthogonal rotation reflection according to scheme 1, characterized in that, for each of the two sub-optical pulses:

The two orthogonal polarization states of the sub-optical pulses of the path are maintained during the beam splitting of the beam splitter to the corresponding reflection device, and are maintained during the reflection of the corresponding reflection device to the beam splitter. constant.

9. The time-bit-phase decoding method for DC modulation quantum key distribution based on polarization orthogonal rotation reflection according to scheme 1, wherein the time-bit decoding of the second optical pulse includes:

Directly output the second optical pulse for detection; or

The second optical pulse is split and output for detection.

10. A time-bit-phase decoding device for DC modulation quantum key distribution based on polarization orthogonal rotation reflection, characterized in that the decoding device comprises:

Pre-beam splitter for splitting an incident input optical pulse of any polarization state into a first optical pulse and a second optical pulse; and,

A DC phase decoder optically coupled to the pre-beam splitter, used for DC phase decoding of the first optical pulse,

The DC phase decoder includes a first beam splitter, two reflecting devices, and two sub-optical paths optically coupled with the first beam splitter and optically coupled with the two reflecting devices, respectively, wherein

The first beam splitter is used to split the first optical pulse into two sub-optical pulses;

The two sub-optical paths are used to transmit the two sub-optical pulses respectively, and are used to realize the relative delay of the two sub-optical pulses;

The two reflecting devices are used to respectively reflect the two sub-light pulses transmitted from the first beam splitter through the two sub-light paths back to the first beam splitter to be split by the first beam splitter Beam combiner output;

Wherein, the two reflection devices are configured such that, for each of the two sub-optical pulses: when the sub-optical pulse is reflected by the corresponding reflection device in the two reflection devices, the sub-optical pulse The two orthogonal polarization states are reflected by the polarization orthogonal rotation, so that after being reflected by the corresponding reflection device, each orthogonal polarization state of the sub-optical pulse of the path is transformed into a polarization state orthogonal thereto,

Wherein the DC phase decoder has a DC phase modulator located on at least one of the two sub-optical paths, the DC phase modulator is used for the sub-optical pulses transmitted through the sub-optical path in accordance with the quantum key distribution protocol Perform DC phase modulation,

The pre-beam splitter uses the second optical pulse output for time-bit decoding.

11. The time-bit-phase decoding device for DC modulation quantum key distribution based on polarization orthogonal rotation reflection according to scheme 10, wherein the two reflection devices are circular polarization orthogonal rotation reflection devices, and the two Each reflecting device includes a reflecting mirror.

12. The time-bit-phase decoding device for DC modulation quantum key distribution based on polarization orthogonal rotation reflection according to scheme 11, wherein the first beam splitter is a circular polarization maintaining beam splitter.

13. The time-bit-phase decoding device for DC modulation quantum key distribution based on polarization orthogonal rotation reflection according to scheme 10, wherein the two reflection devices are linear polarization orthogonal rotation reflection devices.

14. The time-bit-phase decoding device for direct current modulation quantum key distribution based on polarization orthogonal rotation reflection according to scheme 13, wherein the two reflection devices each include a mirror and a quarter wave plate, The mirror is integrally formed with the quarter-wave plate at the rear end of the quarter-wave plate, wherein the quarter-wave plate is constructed such that two of the two sub-light pulses The angle between the polarization direction of one of the orthogonal polarization states and the slow axis of the quarter wave plate is 45 degrees.

15. The time-bit-phase decoding device for direct current modulation quantum key distribution based on polarization orthogonal rotation reflection according to scheme 13, wherein the first beam splitter is a line polarization maintaining beam splitter.

16. The time-bit-phase decoding device for DC modulation quantum key distribution based on polarization orthogonal rotation reflection according to scheme 10, wherein the two reflection devices are elliptical polarization orthogonal rotation reflection devices, and the first A beam splitter is an elliptical polarization maintaining beam splitter.

17. The time-bit-phase decoding device for direct current modulation quantum key distribution based on polarization orthogonal rotation reflection according to scheme 10, wherein the two sub-optical paths are polarization-maintaining optical paths.

18. The time-bit-phase decoding device for DC modulation quantum key distribution based on polarization orthogonal rotation reflection according to scheme 10, wherein the decoding device further includes a second beam splitter, the second beam splitter The optical coupler is optically coupled to the pre-beam splitter for receiving the second optical pulse and splitting the second optical pulse for output for time-bit decoding.

19. A quantum key distribution system, including:

The direct current modulation quantum key distribution time bit-phase decoding device based on polarization orthogonal rotation reflection according to scheme 10, which is provided at the receiving end of the quantum key distribution system and is used for time bit-phase decoding.

The invention achieves unexpected beneficial effects through creative configuration. For the application of time-bit-phase encoding quantum key distribution, the present invention uses polarization orthogonal rotation reflection to control the two orthogonal polarization states of the optical pulse in the phase-based decoding. An orthogonal polarization state effectively interferes with the output at the output port at the same time, thereby implementing the phase-based decoding function of environmental interference immunity, enabling a stable bit-phase encoding quantum key distribution solution for environmental interference immunity. In addition, by splitting the input optical pulse into two optical pulses at the receiving end, the two optical pulses are time-decoded and phase-decoded respectively. In the phase decoding, the optical pulses are DC-selectively modulated, which can advantageously reduce the The requirements related to phase modulation during phase-based decoding during base selection, especially for high-speed systems, avoid the requirement for high-speed phase modulation during base-based decoding. The present invention provides an easy-to-implement and applicable anti-polarization-induced fading time bit-phase coding quantum key distribution solution, while avoiding the need for complex correction equipment, and can be well applied to high-speed quantum cryptography with environmental interference Key distribution application scenario.

BRIEF DESCRIPTION

1 is a flowchart of a time-bit-phase decoding method for DC modulation quantum key distribution based on polarization orthogonal rotation reflection according to a preferred embodiment of the present invention;

2 is a schematic diagram of a composition structure of a time-bit-phase decoding device for DC modulation quantum key distribution based on polarization orthogonal rotation reflection according to a preferred embodiment of the present invention;

FIG. 3 is a schematic diagram of a composition structure of a time-bit-phase decoding device for DC modulation quantum key distribution based on polarization orthogonal rotation reflection according to another preferred embodiment of the present invention;

FIG. 4 is a schematic diagram of a composition structure of a time-bit-phase decoding device for DC modulation quantum key distribution based on polarization orthogonal rotation reflection according to another preferred embodiment of the present invention.

detailed description

The following describes the preferred embodiments of the present invention in detail with reference to the accompanying drawings, where the drawings constitute a part of the present application and are used to explain the principles of the present invention together with the embodiments of the present invention. For the purpose of clarity and simplification, when it may obscure the subject matter of the present invention, a detailed description of the known functions and structures of the devices described herein will be omitted.

A time-bit-phase decoding method of DC modulation quantum key distribution based on polarization orthogonal rotation reflection in a preferred embodiment of the present invention is shown in FIG. 1 and includes the following steps:

Step S101: split an incident input optical pulse of any polarization state into a first optical pulse and a second optical pulse.

The incident input light pulse is in any polarization state, and may be linearly polarized, circularly polarized, or elliptically polarized fully polarized light, or partially polarized light or unpolarized light.

Step S102: Perform DC modulation phase decoding on the first optical pulse and time-bit decode the second optical pulse according to the quantum key distribution protocol.

As will be understood by those skilled in the art, each light pulse can be regarded as composed of two orthogonal polarization states. Naturally, the two sub-optical pulses obtained by splitting one optical pulse can also be regarded as composed of two orthogonal polarization states that are the same as the optical pulse of the same path.

According to the present invention, the DC modulation phase decoding of the first optical pulse may include:

Splitting the first optical pulse into two sub-optical pulses by a beam splitter; and

Transmitting the two sub-optical pulses along the two sub-optical paths respectively, and delaying the two sub-optical pulses relative to each other, then reflecting them back to the beam splitter through two reflecting devices to combine and output the beam splitter, Wherein for each of the two sub-optical pulses:

When the sub-light pulse of this path is reflected by the corresponding reflection device of the two reflection devices, the two orthogonal polarization states of the sub-light pulse of the path are reflected by the polarization orthogonal rotation, so that after reflection by the corresponding reflection device, Each orthogonal polarization state of the pulse is transformed into a polarization state orthogonal thereto.

For example, assuming that these two orthogonal polarization states are the x polarization state and the y polarization state, respectively, the x polarization state transmitted to a reflection device along the optical path is transformed into the orthogonal state after being reflected by the polarization orthogonal rotation at the reflection device The polarization state is the y-polarization state, and the y-polarization state transmitted to the reflecting device along the optical path is converted into the orthogonal polarization state, that is, the x-polarizing state, after being reflected by the orthogonal polarization rotation at the reflecting device.

In this way, using the polarization orthogonal rotation reflection at the reflection device, the x polarization state of each optical pulse obtained by beam splitting is transmitted through the two sub-optical paths during the beam splitting of the beam splitter to the beam splitter. It is exactly equal to the phase difference of the y-polarized state of the optical pulse transmitted through the two sub-optical paths during the splitting of the beam splitter to the beam splitter.

In this method, the two sub-light pulses are reflected by the two reflecting devices odd times or reflected by the two reflecting devices even times (including zero times, that is, direct transmission) and then combined by the beam splitter for output.

In the method of FIG. 1, during the splitting of the beam splitter to the beam splitter, at least one of the two sub-optical pulses transmitted on the two sub-optical paths is distributed according to a quantum key The protocol performs DC phase modulation.

Here, relative delay and phase modulation are carried out in accordance with the requirements and regulations of the quantum key distribution protocol, which will not be described in detail in this article.

According to a possible configuration, the above two reflection devices are circular polarization orthogonal rotation reflection devices. For example, the above two reflecting devices each include a reflecting mirror. In this case, the above beam splitter may be a circular polarization maintaining beam splitter. Here, the circularly polarized orthogonal rotation and reflection device refers to the ability to perform polarization orthogonal rotation and reflection on the incident circularly polarized light, that is, when reflecting the incident circularly polarized light, the polarization state of the circularly polarized light is transformed to be orthogonal to it The polarization device of the polarization state, that is, the incident left-handed circularly polarized light is reflected by the circularly polarized orthogonal rotation reflecting device and then transformed into a right-handed circularly polarized light orthogonal thereto, and the incident right-handed circularly polarized light passes through the circle The polarization orthogonal rotating reflection device is converted into left-handed circularly polarized light orthogonal to it after being reflected.

According to another possible configuration, the above two reflecting devices are linearly polarized orthogonal rotating reflecting devices. For example, the above two reflecting devices each include a mirror and a quarter wave plate, the mirror is integrally formed with the quarter wave plate at the rear end of the quarter wave plate, wherein the The angle between the polarization direction of one of the two orthogonal polarization states of the two sub-light pulses and the fast or slow axis of the quarter wave plate is 45 degrees. In this case, the above beam splitter may be a line polarization maintaining beam splitter. Such a reflection device including a mirror and a quarter-wave plate can be referred to simply as a "quarter-wave plate mirror", which can be achieved by plating a mirror on the surface of the quarter-wave plate crystal, or by The end face of the polarization-maintaining optical fiber with a phase difference of 90 degrees in the axis transmission is plated with a mirror. Here, the linearly polarized orthogonal rotation and reflection device refers to the ability to perform polarization orthogonal rotation and reflection on the incident linearly polarized light, that is, when reflecting the incident linearly polarized light, the polarization state of the linearly polarized light is transformed to be orthogonal to it The polarization device of the polarization state, that is, the incident x-linear polarized light is reflected by the linearly polarized orthogonal rotating reflection device and then transformed into a y-linear polarized light orthogonal thereto, and the incident y-linearly polarized light is positively polarized by the linear After being reflected by the cross-rotating reflection device, it is converted into x-ray polarized light orthogonal thereto.

According to yet another possible configuration, the above two reflecting devices are elliptical polarization orthogonal rotation reflecting devices, and the above beam splitter may be an elliptical polarization maintaining beam splitter. In this case, the appropriate reflecting device can be selected according to the specific elliptical polarization maintaining beam splitter. Here, the elliptical polarization orthogonal rotation and reflection device refers to the ability to perform polarization orthogonal rotation reflection on the incident elliptical polarization state light, that is, when reflecting the incident elliptical polarization state light, the polarization state of the elliptical polarization state light is converted to be orthogonal to it The polarization device of the polarization state, that is, the incident left-handed elliptically polarized light is reflected by the elliptically polarized orthogonal rotation and reflection device and then converted into a right-handed elliptically polarized light orthogonal thereto. The polarized orthogonal rotating reflection device is converted into left-handed elliptical polarized light orthogonal to it after being reflected.

For the above several configurations, advantageously, for each of the two sub-optical pulses in the two sub-optical pulses obtained by splitting the first optical pulse: keep the two orthogonal polarization states of the sub-optical pulses of the path at the beam splitter The beam remains unchanged during reflection to the corresponding reflection device, and remains unchanged during reflection by the corresponding reflection device to the beam splitter. This can be achieved, for example, by configuring the two sub-optical paths as polarization maintaining optical paths and configuring the optical devices on the two sub-optical paths as polarization maintaining optical devices and / or non-birefringent optical devices.

In the method of FIG. 1, performing DC phase modulation on at least one of the two sub-optical pulses transmitted on the two sub-optical paths may include: the two sub-optical pulses transmitted on the two sub-optical paths One of them performs 0 degree DC phase modulation or 180 degree DC phase modulation.

In the method of FIG. 1, time-bit decoding the second optical pulse may include: directly outputting the second optical pulse for detection; or splitting the second optical pulse for output For detection.

A time-bit-phase decoding device for direct current modulation quantum key distribution based on polarization orthogonal rotation reflection in a preferred embodiment of the present invention is shown in FIG. 2 and includes the following components: pre-beam splitter 201 and beam splitter 202 And 206, optical circulator 205, DC phase modulator 207, and two reflecting devices 208 and 209.

Without first considering the optical circulator between the front beam splitter 201 and the beam splitter 206, the decoding device of FIG. 2 includes: a front beam splitter 201; a beam splitter 202; a beam splitter 206, two reflection devices 208 and 209 and two sub-optical paths optically coupled with the beam splitter 206 and optically coupled with the two reflecting devices 208 and 209, respectively. A DC phase modulator 207 is provided on one of the two sub-optical paths. The beam splitter 206, the two reflecting devices 208 and 209, and the two sub-optical paths may be collectively referred to as a DC phase decoder. The two reflecting devices 208 and 209 are each a polarization orthogonal rotating reflecting device.

The front beam splitter 201 is used to split an incident input optical pulse of any polarization state into a first optical pulse and a second optical pulse.

The DC phase decoder is optically coupled with the pre-beam splitter 201, and is used to receive one of the two optical pulses and perform DC modulation phase decoding on it. For convenience, the one-path optical pulse is also referred to as a first-path optical pulse in the following.

The beam splitter 202 is optically coupled with the pre-beam splitter 201, and is used to receive the other optical pulse among the two optical pulses, and split the other optical pulse to output for time-bit decoding. Here, it should be noted that the beam splitter 202 is optional. It is possible that the pre-beam splitter 201 directly outputs the other optical pulse for time-bit decoding.

The DC phase decoder constitutes an unequal-arm Michelson interferometer, in which:

The beam splitter 206 is used to split the first optical pulse into two sub-optical pulses;

The two sub-optical paths are used to transmit the two sub-optical pulses respectively, and are used to realize the relative delay of the two sub-optical pulses;

The DC phase modulator 207 is used to perform DC phase modulation on the sub-optical pulses transmitted through the sub-optical path in accordance with the quantum key distribution protocol;

The two reflecting devices 208 and 209 are used to respectively reflect the two sub-light pulses transmitted from the beam splitter 206 through the two sub-optical paths back to the beam splitter to be combined and output by the beam splitter.

Since the two reflecting devices 208 and 209 are polarization orthogonal rotating reflecting devices, for each of the two sub-light pulses obtained by splitting the first optical pulse: the sub-light pulse passes through the two reflecting devices When reflected by the corresponding reflection device in the two orthogonal polarization states of the sub-optical pulse of the path, the polarization orthogonal rotation is reflected, so that after reflection through the corresponding reflection device, each orthogonal polarization state of the sub-optical pulse of the path is transformed into its Orthogonal polarization.

The relative delay of the two sub-optical pulses can be achieved by adjusting the physical length of any one of the two sub-optical paths between the beam splitter 206 and the two reflecting devices 208, 209.

The DC phase modulator 207 can modulate a 0 degree phase or a 180 degree phase. The DC phase modulator 207 may be a polarization-independent phase modulator or a polarization-dependent phase modulator, such as a polarization-maintaining fiber stretcher or a birefringence phase modulator.

The polarization-independent phase modulator is suitable for performing the same phase modulation on the two orthogonal polarization states of the optical pulse, so it is called polarization-independent. For example, the polarization-independent phase modulator can be implemented by two birefringent phase modulators connected in series or in parallel. According to the situation, the DC phase modulation of the optical pulse can be achieved by various specific means. For example, these measures may include: modulating the length of the free-space optical path, or modulating the length of the optical fiber, or using series or parallel optical waveguide phase modulators. For example, the desired DC phase modulation can be achieved by changing the length of the free-space optical path with a motor. As another example, the length of the optical fiber can be modulated by an optical fiber stretcher using the piezoelectric effect, thereby achieving phase modulation. In addition, the phase modulator can be other types suitable for voltage control. By applying a suitable DC voltage to the polarization-independent phase modulator to perform the same phase modulation on the two orthogonal polarization states of the optical pulse, the desired DC phase can be achieved modulation. In the case of DC phase modulation, there is no need to convert the voltage applied to the phase modulator.

A polarization-dependent phase modulator, such as a birefringence phase modulator, is suitable for applying different adjustable phase modulations to the two orthogonal polarization states passing through it. For example, the birefringent phase modulator may be a lithium niobate phase modulator, and by controlling the voltage applied to the lithium niobate crystal, the phase modulation experienced by each of the two orthogonal polarization states passing through the lithium niobate phase modulator Perform control and adjustment.

The above DC phase decoder can optionally have the following settings:

a) The two reflecting devices 208 and 209 are circular polarization orthogonal rotating reflecting devices. For example, the two reflecting devices 208 and 209 each include a mirror; the beam splitter 206 is a circular polarization maintaining beam splitter.

b) The two reflecting devices 208 and 209 are linearly polarized orthogonal rotating reflecting devices. For example, the two reflecting devices 208 and 209 each include a mirror and a quarter-wave plate. The rear end of the plate is formed integrally with the quarter wave plate, wherein the polarization direction of one of the two orthogonal polarization states of the two sub-light pulses and the fast axis of the quarter wave plate or The angle of the slow axis is 45 degrees; the beam splitter 206 is a line polarization maintaining beam splitter.

c) The two reflecting devices 208 and 209 are elliptical polarization orthogonal rotating reflecting devices; the beam splitter 206 is an elliptical polarization maintaining beam splitter. In this case, the appropriate reflecting device can be selected according to the specific elliptical polarization maintaining beam splitter.

In the case where the settings a), b) or c) are adopted, advantageously, in the DC phase decoder, for each of the two sub-optical pulses obtained by splitting the first optical pulse: keep this sub-pulse The two orthogonal polarization states of the optical pulse remain unchanged during the beam splitting of the beam splitter to the corresponding reflection device, and remain unchanged during the reflection of the corresponding reflection device to the beam splitter. This can be achieved, for example, by configuring the two sub-optical paths as polarization maintaining optical paths and configuring the optical devices on the two sub-optical paths as polarization maintaining optical devices and / or non-birefringent optical devices.

The unequal-arm Michelson interferometer constituted by the DC phase decoder may be a polarization-maintaining unequal-arm Michelson interferometer or a non-polarization unequal-arm Michelson interferometer, depending on the specific configuration.

As shown, the device of FIG. 2 also includes an optical circulator 205. The optical circulator 205 is located in front of the beam splitter 206 of the DC phase decoder. In this case, one of the input port and output port of the unequal-arm Michelson interferometer constituted by the DC phase decoder is the same port. The first optical pulse from the pre-beam splitter 201 can be input from the first port A of the optical circulator 205 and output from the second port B of the optical circulator 205 to the beam splitter 206. The beam output may be input to the second port B of the optical circulator 205 and output from the third port C of the optical circulator 205.

A time-bit-phase decoding device for DC modulation quantum key distribution based on polarization orthogonal rotation reflection according to another preferred embodiment of the present invention is shown in FIG. 3 and includes the following components: beam splitters 303 and 304, and optical circulator 307, a polarization maintaining beam splitter 308, a DC phase modulator 309, and mirrors 310 and 311. The polarization-maintaining beam splitter 308 is a circular polarization-maintaining optical fiber beam splitter.

The beam splitter 303 serves as a front beam splitter, and one of the two ports 301 and 302 on one side thereof serves as an input port of the device. The beam splitter 304 splits one optical pulse from the beam splitter 303 and outputs it to the port 305 or 306. The optical pulse input from the first port A of the optical circulator 307 is output from the second port B of the optical circulator 307, and the optical pulse input from the port B of the optical circulator 307 is output from the third port C of the optical circulator 307. The polarization-maintaining beam splitter 308 and the mirrors 310, 311 constitute a polarization-maintaining unequal-arm Michelson interferometer, and the two sub-optical pulses in between are polarization-maintaining optical fiber optical paths. The DC phase modulator 309 is inserted into either arm of the polarization maintaining unequal-arm Michelson interferometer. The optical pulse input to the polarization-maintaining unequal-arm Michelson interferometer is output by the port 312 after being decoded, or transmitted to the port B of the optical circulator 307 through another output port of the polarization-maintaining beam splitter 308 and from the optical circulator 307 ’s After port C is output, it is output by port 313.

In operation, the input optical pulse enters the beam splitter 303 through the port 301 or 302 of the beam splitter 303, and is split into two optical pulses by the beam splitter 303 for transmission. An optical pulse from the beam splitter 303 is input to the beam splitter 304, and is split by the beam splitter 304, and then output by the port 305 or 306 for time-bit decoding. Another optical pulse from the beam splitter 303 is input through the port A of the optical circulator 307 and output from the port B of the optical circulator 307 to the polarization maintaining beam splitter 308. The polarization maintaining beam splitter 308 splits the other optical pulse into two sub-optical pulses. One sub-pulse pulse is modulated by the DC phase modulator 309 to 0-degree phase or 180-degree phase, and then reflected by the mirror 310. The other sub-pulse pulse is directly transmitted to the mirror 311 through the polarization-maintaining fiber and reflected back by the mirror 311. The reflected two relatively delayed sub-optical pulses are combined by the polarization maintaining beam splitter 308 and output from the port 312, or transmitted to the port B of the optical circulator 307 and output from the port C of the optical circulator 307, and then output by the port 313 output.

A time-bit-phase decoding device for DC modulation quantum key distribution based on polarization orthogonal rotation reflection according to another preferred embodiment of the present invention is shown in FIG. 4 and includes the following components: beam splitters 403 and 404, optical circulator 407, a polarization maintaining beam splitter 408, a DC phase modulator 409, and quarter wave plate mirrors 410 and 411. The quarter-wave plate mirrors 410 and 411 can be implemented by quarter-wave plate crystal surface-coated mirrors, or can be realized by polarization-maintaining fiber end-face mirrors with a phase difference of 90 degrees between the fast and slow axis transmission phases. The angle between the fast axis or slow axis of the polarization-maintaining fiber connected to the quarter-wave plate mirrors 410 and 411 and the corresponding fast axis or slow axis of the quarter-wave plate is 45 degrees. The polarization-maintaining beam splitter 408 is a line polarization-maintaining optical fiber beam splitter.

The beam splitter 403 serves as a front beam splitter, and one of the two ports 401 and 402 on one side thereof serves as an input port of the device. The beam splitter 404 splits one optical pulse from the beam splitter 403 and outputs it to the port 405 or 406. The optical pulse input from the first port A of the optical circulator 407 is output from the second port B of the optical circulator 407, and the optical pulse input from the port B of the optical circulator 407 is output from the third port C of the optical circulator 407. The polarization-maintaining beam splitter 408 and the quarter-wave plate mirrors 410 and 411 form a polarization-maintaining unequal-arm Michelson interferometer, and the two sub-optical paths therebetween are polarization-maintaining optical fiber optical paths. The DC phase modulator 409 is inserted into either arm of the polarization maintaining unequal-arm Michelson interferometer. The optical pulse input to the polarization-maintaining unequal-arm Michelson interferometer is output through port 412 after being decoded, or transmitted to the port B of the optical circulator 407 through the other output port of the polarization-maintaining beam splitter 408 and from the port of the circulator 407 After C is output, it is output by port 413.

During operation, the input optical pulse enters the beam splitter 403 through the port 401 or 402 of the beam splitter 403, and is split by the beam splitter 403 into two optical pulses for transmission. An optical pulse from the beam splitter 403 is input to the beam splitter 404, and is split by the beam splitter 404, and then output by the port 405 or 406 for time-bit decoding. Another optical pulse from the beam splitter 403 is input through the port A of the optical circulator 407 and output from the port B of the optical circulator 407 to the polarization maintaining beam splitter 408. The polarization maintaining beam splitter 408 splits the other optical pulse into two sub-optical pulses. One sub-optical pulse is modulated by the DC phase modulator 409 to 0-degree phase or 180-degree phase, and then reflected by the quarter-wave plate mirror 410, and the other sub-optical pulse is directly transmitted to the quarter-wave plate through the polarization-maintaining fiber The mirror 411 is reflected back by the quarter-wave plate mirror 411. The two relatively delayed sub-optical pulses reflected back are combined by the polarization maintaining beam splitter 408 and output from the port 412, or transmitted to the port B of the optical circulator 407 and output from the port C of the optical circulator 407, and then output by the port 413 output.

Herein, the terms "beam splitter" and "beam combiner" are used interchangeably, and the beam splitter may also be called and used as a beam combiner, and vice versa. In this article, "polarization-maintaining optical fiber optical path" refers to an optical path that uses polarization-maintaining optical fibers to transmit optical pulses or an optical path formed by connecting polarization-maintaining optical fibers.

The direct current modulation quantum key distribution time bit-phase decoding device based on polarization orthogonal rotation reflection of the present invention can be configured at the receiving end of the quantum key distribution system for time bit-phase decoding. In addition, the DC-modulated quantum key distribution time bit-phase decoding device based on polarization orthogonal rotation reflection of the present invention may also be configured at the transmitting end of the quantum key distribution system for time bit-phase encoding.

Through the description of the specific embodiments, it should be possible to have a more in-depth and specific understanding of the technical means and functions adopted by the present invention to achieve the intended purpose. However, the accompanying drawings are only for reference and explanation, not for the purpose of applying the present invention. limit.

Claims (19)

1. A time-bit-phase decoding method for DC modulation quantum key distribution based on polarization orthogonal rotation reflection, characterized in that the method includes:

   Split an incident input optical pulse of any polarization state into a first optical pulse and a second optical pulse; and

   According to the quantum key distribution protocol, performing DC modulation phase decoding on the first optical pulse and time-bit decoding the second optical pulse,

   Wherein, the DC modulation phase decoding of the first optical pulse includes:

   Splitting the first optical pulse into two sub-optical pulses by a beam splitter; and

   Transmitting the two sub-optical pulses along the two sub-optical paths respectively, and delaying the two sub-optical pulses relative to each other, then reflecting them back to the beam splitter through two reflecting devices to combine and output the beam splitter, Wherein for each of the two sub-optical pulses:

   When the sub-light pulse of this path is reflected by the corresponding reflection device of the two reflection devices, the two orthogonal polarization states of the sub-light pulse of the path are reflected by the polarization orthogonal rotation, so that after reflection by the corresponding reflection device, the sub-light pulse Each orthogonal polarization state of the pulse is transformed into its orthogonal polarization state,

   And wherein, during the splitting of the beam splitter to the beam splitter, at least one of the two sub-optical pulses transmitted on the two sub-optical paths is subjected to a DC phase according to a quantum key distribution protocol modulation.
2. The time-bit-phase decoding method for DC modulation quantum key distribution based on polarization orthogonal rotation reflection according to claim 1, wherein the two reflection devices are circular polarization orthogonal rotation reflection devices, and the two The reflecting devices each include a reflecting mirror.
3. The time-bit-phase decoding method for DC modulation quantum key distribution based on polarization orthogonal rotation reflection according to claim 2, wherein the beam splitter is a circular polarization maintaining beam splitter.
4. The time-bit-phase decoding method for DC modulation quantum key distribution based on polarization orthogonal rotation reflection according to claim 1, wherein the two reflection devices are linear polarization orthogonal rotation reflection devices.
5. The time-bit-phase decoding method for DC modulation quantum key distribution based on polarization orthogonal rotation reflection according to claim 4, wherein the two reflection devices each include a mirror and a quarter wave plate, so The mirror is formed integrally with the quarter-wave plate at the rear end of the quarter-wave plate, wherein the polarization direction of one of the two orthogonal polarization states of the two sub-light pulses is The angle of the slow axis of the quarter wave plate is 45 degrees.
6. The time-bit-phase decoding method for DC modulation quantum key distribution based on polarization orthogonal rotation reflection according to claim 4, wherein the beam splitter is a line polarization maintaining beam splitter.
7. The time-bit-phase decoding method for DC modulation quantum key distribution based on polarization orthogonal rotation reflection according to claim 1, wherein the two reflection devices are elliptical polarization orthogonal rotation reflection devices, and the beam splitting The filter is an elliptical polarization maintaining beam splitter.
8. The time-bit-phase decoding method for DC modulation quantum key distribution based on polarization orthogonal rotation reflection according to claim 1, wherein, for each of the two sub-optical pulses:

   The two orthogonal polarization states of the sub-optical pulses of the path are maintained during the beam splitting of the beam splitter to the corresponding reflection device, and are maintained during the reflection of the corresponding reflection device to the beam splitter. constant.
9. The time-bit-phase decoding method for DC modulation quantum key distribution based on polarization orthogonal rotation reflection according to claim 1, wherein time-bit decoding of the second optical pulse comprises:

   Directly output the second optical pulse for detection; or

   The second optical pulse is split and output for detection.
10. A time-bit-phase decoding device for DC modulation quantum key distribution based on polarization orthogonal rotation reflection, characterized in that the decoding device includes:

    Pre-beam splitter for splitting an incident input optical pulse of any polarization state into a first optical pulse and a second optical pulse; and,

    A DC phase decoder optically coupled to the pre-beam splitter, used for DC phase decoding of the first optical pulse,

    The DC phase decoder includes a first beam splitter, two reflecting devices, and two sub-optical paths optically coupled with the first beam splitter and optically coupled with the two reflecting devices, respectively, wherein

    The first beam splitter is used to split the first optical pulse into two sub-optical pulses;

    The two sub-optical paths are used to transmit the two sub-optical pulses respectively, and are used to realize the relative delay of the two sub-optical pulses;

    The two reflecting devices are used to respectively reflect the two sub-light pulses transmitted from the first beam splitter through the two sub-light paths back to the first beam splitter to be split by the first beam splitter Beam combiner output;

    Wherein, the two reflection devices are configured such that, for each of the two sub-optical pulses: when the sub-optical pulse is reflected by the corresponding reflection device in the two reflection devices, the sub-optical pulse The two orthogonal polarization states are reflected by the polarization orthogonal rotation, so that after being reflected by the corresponding reflection device, each orthogonal polarization state of the sub-optical pulse of the path is transformed into a polarization state orthogonal thereto,

    Wherein the DC phase decoder has a DC phase modulator located on at least one of the two sub-optical paths, the DC phase modulator is used for the sub-optical pulses transmitted through the sub-optical path in accordance with the quantum key distribution protocol Perform DC phase modulation,

    The pre-beam splitter uses the second optical pulse output for time-bit decoding.
11. The direct current modulation quantum key distribution time bit-phase decoding device based on polarization orthogonal rotation reflection according to claim 10, wherein the two reflection devices are circular polarization orthogonal rotation reflection devices, and the two The reflecting devices each include a reflecting mirror.
12. The time-bit-phase decoding device for DC modulation quantum key distribution based on polarization orthogonal rotation reflection according to claim 11, wherein the first beam splitter is a circular polarization maintaining beam splitter.
13. The direct current modulation quantum key distribution time bit-phase decoding device based on polarization orthogonal rotation reflection according to claim 10, wherein the two reflection devices are linear polarization orthogonal rotation reflection devices.
14. The time-bit-phase decoding device for DC modulation quantum key distribution based on polarization orthogonal rotation reflection according to claim 13, wherein the two reflection devices each include a mirror and a quarter wave plate, so The mirror is integrally formed with the quarter-wave plate at the rear end of the quarter-wave plate, wherein the quarter-wave plate is constructed such that two of the two sub-light pulses The angle between the polarization direction of one of the orthogonal polarization states and the slow axis of the quarter wave plate is 45 degrees.
15. The time-bit-phase decoding device for direct current modulation quantum key distribution based on polarization orthogonal rotation reflection according to claim 13, wherein the first beam splitter is a line polarization maintaining beam splitter.
16. The time-bit-phase decoding device for DC modulation quantum key distribution based on polarization orthogonal rotation reflection according to claim 10, wherein the two reflection devices are elliptical polarization orthogonal rotation reflection devices, and the first The beam splitter is an elliptical polarization maintaining beam splitter.
17. The time-bit-phase decoding device for DC modulation quantum key distribution based on polarization orthogonal rotation reflection according to claim 10, wherein the two sub-optical paths are polarization-maintaining optical paths.
18. The time-bit-phase decoding device for direct current modulation quantum key distribution based on polarization orthogonal rotation reflection according to claim 10, wherein the decoding device further comprises a second beam splitter, the second beam splitter Optically coupled to the pre-beam splitter, for receiving the second optical pulse and splitting the second optical pulse for output for time-bit decoding.
19. A quantum key distribution system, including:

    The direct current modulation quantum key distribution time bit-phase decoding device based on polarization orthogonal rotation reflection according to claim 10, which is provided at the receiving end of the quantum key distribution system and is used for time bit-phase decoding.

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